1. Field of the Invention
The present invention relates to image processing apparatuses and methods for printing and plate making, and more specifically to technology for trapping between objects including image objects (data).
2. Description of the Background Art
In the field of printing and plate making, a personal computer or such like is used to first perform an edit process based on characters that are to be contained in a print and a plurality of types of other print elements, such as logos, patterns, and illustrations, and generate page data containing a print target written in a page-description language. Thereafter, a RIP process is performed on the page data to generate image data for use in production of a plate (a press plate) that is to be placed in a printing machine.
Incidentally, in the case of multicolor printing, in order to prevent an underlying portion from being exposed at a boundary between colors due to misregistration, a trapping process is performed before the performance of the RIP process on the page data. The trapping process is to dispose, along a boundary portion between two adjacent colors on an image, a hairline graphic (hereinafter, referred to as a “trap graphic”) which has a color containing color elements from both sides of the boundary portion. For example, in the case where a Y color halftone tint object 71, a C color halftone tint object 72, and an M color halftone tint object 73 are located so as to overlap with each other as shown in FIG. 16A, for example, the trapping process generates trap graphics 74 to 76 in boundary portions between the overlapping objects as shown in FIG. 16B. As a result, any underlying portion is prevented from being exposed in boundary portions between colors due to misregistration in the case of multicolor printing.
In the above-described trapping process for objects with colored line drawing such as halftone tints, strokes and characters (such objects, for which a plurality of colorplates are used, are referred to hereinafter as “color objects”), a value (a luminance level) that represents brightness is calculated for each color object, and thereafter the trap graphic is generated on a color object at a lower luminance level, i.e., a relatively dark-colored object. This makes the trap graphic less noticeable, preventing image quality from being reduced by the trapping process.
On the other hand, in the trapping process between image objects (hereinafter simply referred to as “images”) or between an image and a color object, the luminance level of each image varies from one pixel to another, and therefore the side on which a trap graphic is to be generated (hereinafter, referred to as a “trap direction”) cannot be determined from among the two objects according to the luminance levels. Thus, for example, the trap direction is determined according to a trap rule designated by the user from among preset trap rules (rules for automatically determining the trap direction).
Examples of the trap rules between the image and the color object include “no trap graphic”, “increase in area of color object relative to image”, “decrease in area of color object relative to image”, “centering”, etc. Note that each of the trap rules can be designated per (color object) type, such as halftone tint, stroke, or character (e.g., “the halftone tint can be increased in area relative to the image”). In addition, examples of the trap rules between images include “no trap graphic”, “increase in area of top (front) image relative to bottom (back) image”, “decrease in area of top (front) image relative to bottom (back) image”, “centering”, etc.
Trap graphics generated according to the trap rules will be described with reference to FIGS. 17A to 17D. Note that FIGS. 17A to 17D provide illustrations based on the assumption that an image 81 and a color object (here, a halftone tint) 82 are disposed so as to be a bottom (back) image and a top (front) image, respectively. In the case where “no trap graphic” is designated from among the above-described trap rules, no trap graphic is generated as shown in FIG. 17A. In the case where “increase in area of color object relative to image” is designated, a trap graphic 83 is generated on the image 81 as shown in FIG. 17B. In the case where “decrease in area of color object relative to image” is designated, a trap graphic 84 is generated on the color object 82 as shown in FIG. 17C. In the case where “centering” is designated, a trap graphic 85 is generated centering around the boundary between the image 81 and the color object 82 as shown in FIG. 17D.
Note that the following techniques have been disclosed in relation to the trapping process. Japanese Laid-Open Patent Publication No. 2004-34636 discloses a technique related to a trapping process for use in the case where black characters overlap a design. Japanese Laid-Open Patent Publication No. 2006-5481 discloses a technique for predicting a direction in which a plate significantly deviates, and setting a wide trap width in that direction. Japanese Laid-Open Patent Publication No. 2004-122692 discloses a technique for changing the size of a trap area depending on printing methods. Japanese Laid-Open Patent Publication No. 2001-129986 discloses a technique for eliminating variations between printing and proofing in terms of the accuracy of trapping and the degree of garbling. Japanese Laid-Open Patent Publication No. 2003-87548 discloses a technique related to a trapping process for a document with a plurality of pages. Japanese Laid-Open Patent Publication No. 2004-155001 discloses a technique related to a trapping process between graphics. Japanese Laid-Open Patent Publication No. 2006-202198 discloses a technique for speeding up a trapping process. Japanese Laid-Open Patent Publication No. 2006-129007 discloses a technique for speeding up a trapping process using an object-type-information bitmap, and a processing parameter per object, as well as allowing the user to readily designate a trapping parameter.
However, when the trapping process is automatically carried out between images or between an image and a color object according to the above-described trap rules, a trap graphic might be generated in an undesirable direction. Such a case will be described with reference to FIGS. 18A and 18B, as well as FIGS. 19A and 19B. Note that in FIGS. 18A, 18B, 19A, and 19B, for ease of explanation, the trap graphic is depicted in bold and dark color.
The first assumption is that relatively dark color objects (a halftone tint, 92 and characters 93) are disposed on (in front of) a relatively bright image 91 prior to the trapping process as shown in FIG. 18A. In this case, if the trap rule “increase in area of color object relative to image” is designated, the trapping process produces a result as shown in FIG. 18B. Specifically, a trap graphic is generated in an undesirable direction, so that the trap graphic is significantly noticeable.
The next assumption is that relatively bright color objects (a halftone tint 95 and characters 96) are disposed on (in front of) a relatively dark image 94 prior to the trapping process as shown in FIG. 19A. In this case, if the trap rule “decrease in area of color object relative to image” is designated, the trapping process produces a result as shown in FIG. 19B. Specifically, a trap graphic is generated in an undesirable direction, so that the halftone tint and the characters are unclear.
In addition, when the data as shown in FIG. 18A and the data as shown in FIG. 19A coexist within a single page, the conventional trap rules do not “allow a trap graphic to be generated in a desirable direction for all objects”.
As described above, when the trapping process is automatically carried out between objects including an image, a trap graphic might not be generated in a desirable direction, leading to a reduction in image quality. In addition, the user is required to manually correct any portion in which the trap graphic is generated in an undesirable direction, leading to a reduction in working efficiency.